Light-sensitive system



July 26, 1938. o. D. KNOWLES LIGHT SENSITIVE SYSTEM Filed April 25. 1930E a p ww T n WK 0 [Z I k W m P D ATTORNEY Patented Jul 26, 1938 UNITEDSTATES PATENT OFFICE LIGHT- SENSITIVE SYSTEM Application April 23, 1930,Serial No. 446,482

9 Claims.

My present application is a continuation, in part, of my pendingapplication, Serial No. 149,290, filed Nov. 19, 1926, and assigned toWestinghouse Electric 8: Manufacturing Company,

that deals, in particular, with electronic relays. The present inventionrelates to improvements in light-sensitive apparatus of which anelectronic relay forms an essential element, and it has particularrelation to devices of this type wherein means is provided for varyingthe sensitivity.

Light-sensitive apparatus, of this nature, constructed according to theteachings of the prior art, with which I am familiar, comprises,chiefly,

an electronic relay actuated from a source of power and controlled by aplurality of lightsensitive cells.

It often happens that apparatus is used in localities where the powersupply is not constant but has comparatively large periodic and randomfluctuations. These variations seriously impair the utility of theapparatus, since account of them must be taken in designing theapparatus, and, as a result, a comparatively large margin must beprovided over which the system does not operate. In the presenttraflic-control systems, wherein equipment of this nature is provided asthe operating element, a variation of i 48% in the light flux eii'ectingthe photo-cells is required.

It is, accordingly, an object of my invention to provide light-sensitiveapparatus the sensitivity of which is adjustable.

Another object of my invention is to provide,

5 in light-sensitive apparatus, means for compensating for variations inthe operating potential.

An additional object of my invention is to provide a gaseous relay, theresponse of which is,

within predetermined limits, independent of the 40 value of thedifference of potential supplied between the electrodes thereof.

It is still another object of my invention to provide an electronicrelay wherein the value of the potential difference required to cause adis- 45 charge between the cathode and the anode increases as thepotential dlfierence between these two electrodes is increased.

More specifically stated, it is an object of my invention to provide, inlight-sensitive apparatus 50 of the type incorporating an electronicrelay,

an impedance disposed between the control electrode and one principalelectrode of the relay, and responsive to variations in theelectromotive force applied to the principal electrodes of the 55 relay.

According to one modification of my invention, I provide alight-sensitive system comprising an electronic relay, a plurality ofphoto-cells and a variable impedance. The principal electrodes of therelay are connected to the terminals 5 of a power source, thephoto-cells provide a potential conductive path between one principalelectrode and the control electrode of the relay, and the impedance isconnected between the remaining principal electrode and the controlelec- 10 trode. The impedance is, furthermore, responsive tofluctuations in the power source and varies therewith, thus varying theillumination required to actuate the relay.

In a more specific application of my inven- 15 tion, the variableimpedance comprises a photocell energized by a source of light heatedfrom the same power supply that yields the voltage for the electronicrelay.

The novel features that I consider character'- 20 istic of my inventionare set forth with particularity in the appended claims. The inventionitself, however, both as to its organization and its method ofoperation, together with additional objects and advantages thereof, willbest be un- 25 derstood from the following description of specificembodiments, when read in connection with the accompanying drawing inwhich;

Figure 1 is a view, partly in elevation and partly in section, of thedischarge tube described 30 in my copending application to whichreference was hereinabove made.

Fig. 2 is a schematic drawing showing a circuit from which my inventionhas been develp Fig. 3 is a schematic drawing showing the general formthat a circuit comprising my invention takes,

Fig. 4 is a schematic drawing showing a general form of my improvedapparatus,

Fig. 5 is a graph that will be utilized in describing the theoreticalbasis of my improvement,

and

Fig. 6 is aschematic drawing showing a specific form of my improvedapparatus.

The apparatus shown in Fig. 1 comprises a glass envelope l having apress 2 mounted therein from which are supported a cylindrical cathode 3and a central anode 4. The anode 4 is surrounded by a glass tube 5 whichis either continuous with, or is welded to, the material of the press 2.A metallic screen element 6 surrounds the glass tube 5 and fits closelyover the upper end of the anode 4.

The tube contains an inert gas, such as argon or neon, at a pressure oiapproximately 2 millimeters of Hg, and the screen element 6 is separatedfrom the anode by a distance preferably less than the mean-free-path ofan electron in the gas, at this pressure.

Suitable conducting leads I, 8 and 9 extend from the various electrodesto the exterior of the tube and are connected to a plurality of contactposts l0, H, I! carried by a base element 13 into which the tube iscemented.

The cathode 3 and the anode 4 are customarily designated as theprincipal electrodes of the dischargetube, while the screen element 6 istermed the control electrode or grid.

It is well to mention here that the separation between the screenelement 6 and the anode 4 is more than an academic matter related to thekinetic theory of gases, in this connection, and has distinct physicalsignificance. It is a well established experimental fact that theelectromotive force required to cause a disruptive discharge between twoelectrodes of a gaseous discharge is not a permanently decreasingfunction of the distance between the electrodes but has a minimum valuefor a certain distance between the electrodes and rapidly increases,thereafter, as the distance between the electrodes is decreased.Quantitative comparisons between the electrode spacing at which thebreak-down voltage begins to increase, and values of the meanfree pathof an electron in the gas between the electrodes, determined fromindependent physical considerations, have established the predictionthat the two values are approximately equivalent.

The explanation of the phenomenon from the standpoint of the kinetictheory of gases is simple. Physically, the mean-free path is simply someform of the mean distance between two successive collisions of a randomelectron in the gas. One of the principal active elements in producing adisruptive discharge is the ionization eiTected by the collisionsbetween the molecules and the electrons. By decreasing the probabilityof collision, the contribution of molecular ionization toward eflectinga break-down of the tube is decreased and, consequently, the differencein potential that must be applied between the principal electrodes tocause a discharge is correspondingly increased.

In view of the above explanation, it is seen that, in a discharge tubeof the type described hereinabove, the drop in potential, between thecathode andthe grid 6, that is required to cause a disruptive discharge,may be considerably smaller than the corresponding drop in potentialbetween the grid 6 and anode 4.

In operation, impedances l5 and I6 are connected between each principalelectrode and the control electrode of the tube, and a difierence ofpotential is applied by a generator ll between the principal electrodesof the tube.

Let Za be the impedance l5 between the anode 4 and the control electrode6, and Zc be the impedance l6 between the cathode 3 and the controlelectrode 6. The drop in potential between each of the principalelectrodes 3 and 4 and the control electrode 6 is dependent on Za andZn.

If Z3 is large and Zn is small, the drop in potential between the anode4 and the control electrode 6 is large, while the drop in potentialbetween the cathode 3 and the control electrode 6 is small. As a result,the electron current drawn from the cathode 3 to the control electrode 6is small, and a disruptive discharge does not take place between the twoelectrodes 3 and 4. 0n the other hand, the distance between the controlelectrode anode 4 and the grid 6 is small.

6 and the anode 4 is less than the mean-freepath of the electrons in thegas, and, consequently, the collisions that take place in the gasbetween these two electrodes is not sufllcient to cause a disruptivedischarge between these elec-. trodes. The tube is then virtuallynon-conductive.

If, however, Zc'iS large and Z9. is small, the drop in potential betweenthe cathods 3 and the grid 6 is large, and the drop in potential betweenthe It Zc is large enough, suflicient drop in potential may exist between the cathode 3 and the control electrode 6 to cause a dischargetherebetween.

The gas column through which the discharge takes place is now in ahighly ionized state and, consequently, theimpedance between the oathode3 and the grid 6 is relatively small. Virtually, the total electromotiveforce E is, therefore, now applied between the grid 6 and the anode 4and, as a result, the insulating gas between the grid and the anodebreaks down, and a heavy current flows through the tube.

The impedance Zc between the cathode 3 and the control electrode 6,necessary to cause a discharge in the tube, depends on the drop inpotential between the principal electrodes 3 and 4 and on impedance Zc.As the drop in potential between the principal electrodes increases, thevalue of impedance Zc that is necessary to cause a discharge in the tubedecreases.

It should be noted that, if the control electrode 6 is entirelyinsulated from the anode 4 and the cathode 3, the first flow of electroncurrent from the cathode results in an accumulation of electrons on thecontrol electrode and causes it to block the flow of further electroncurrent.

In Fig. 2, an arrangement of the apparatus is shown whereby a dischargetube I may be operated. In this case, the control electrode is, undernormal circumstances, insulated from both the anode andthe cathode. Thatis to say, the impedances between the electrodes are very large.Electrons flowing from the cathode 3, therefore, collect on the controlelectrode 6 and establish a negative potential blocking the flow offurther electrons therefrom.

To provide for the leakage of the electrons from the control electrode6, a photo-electric cell I9 is connected between the electrode 3 and theground 20. The anode 2| of the cell I9 is connected to ground 20 and thecathode 22 to the grid 6 of the tube. The grid circuit is completedthrough the distributed-capacity-to-ground 23 of the secondary 24 of thetransformer 25, which tial is established between the grid and thecathode 3 which results in a break-down of the tube I. As shown in Fig.2, the discharge current excites a relay 21 which, as a matter of fact,may symbolize any signalling device.

In the apparatus shown in Fig. 3 and other apparatus constructedaccording to the teachings of the prior art, of which I am aware,provision is not made for taking care of variations in the impressedvoltage. As a result, when the tube I is not operating, the photo-cell28 must be under the influence of a light flux determined by the maximumvalue of the voltage and not by its average value. The difie-rencebetween the light flux necessary to operate the tube and the light fluxunder which it does not operate is. therefore, materially increased.

In Fig. 4, the apparatus that I provide to remedy the situation is shownin detail. The apparatus shown in the drawing comprises, in addition tothe electronic relay I and the source of potential I'l connected to itselectrodes 3 and 4, a photo-electric cell 28 connected between the grid8 and the anode 4, a variable impedance 28 connected between the grid 6and the cathode 3, and an impedance 30 connected in series with thesource of. potential II.

The function of the impedance 38 in the power line I1 is simply to limitthe current that flows through the tube I. The variable impedance 28, onthe other hand, is responsive to variations in the impressed potential,and decreases as the electromotive force of the source II increases. Itis representative of a ballast tube or a photocell 32 connected as shownin Fig. 6 that will presently be explained.

In Fig. 5, the relation between the illumination on the photo-cell andthe impressed voltage,

necessary to cause a discharge in the tube relay, is shown graphically.The curve on the left 34 is plotted for a certain value of impedance 28between the cathode 3 and the control electrode 8, and the curve on theright 35 is plotted for a smaller value of the impedance 29. It is seenthat the voltage E1, necessary to cause a discharge in the tube, at agiven intensity of illumination Io, increases as the impedancedecreases. A potential difference E2 greater than E1 must be appliedbetween the principal electrodes of the tube to operate it with thesmaller impedance 29 between the grid 8 and the cathode 3.

It is seen then that, if. the impedance 28 is responsive to the voltagefluctuations between the principal electrodes 3 and 4, thecharacteristic of the tube I itself becomes responsive to the variationsin the voltage, and compensation of the irregularity of the source I1 iseffected. It is thus possible to operate my improved lightsensitiveapparatus between considerably smaller limits of intensity of theillumination efiecting the photo-cell 28 than is possible with theearlier apparatus.

It is to be noted that, in the apparatus shown in Fig. 4, the tube I isactive when the photoelectric cell 28 is in an energized state. If theanode 2| of the photo-cell is connected to the grid 8, instead of theanode 4 of the tube, and the cathode 22 is connected to the cathode 3 ofthe tube, a system is obtained wherein the discharge I is inactive whenthe photo-cell 28 is energized. In this case, the impedance 29 isconnected between the grid 8 and the anode 4 and responds to the voltageE by increasing therewith. A system of this type is within the scope of.my invention.

Also within the scope of my invention, is a system wherein a pluralityof cells 28 are used instead of a single cell 28. These cells may, ofcourse, have any predetermined arrangement in the circuit.

Furthermore, I may point out that my system is operable with directcurrent as well as with alternating current. The condenser 28 in thedrawing, which represents the impedance is, therefore, to be regarded asonly symbolical.

Finally, it should be noted that it is within the province of myinvention to connect the anode 2| of the photo-cell 28 and the lowerterminal of the impedance 28 to the terminals of the power .tween thecontrol electrode 8 and the cathode 3 and is under the influence of asecond source of light 38, also operated from the transformer 48.

It is to be noted that, in apparatus of this nature designed accordingto the teachings of the prior art, the second photo-cell 32 and the lamp38 are replaced by a constant impedance. In this case, an increase inthe voltage in the primary 4| of the transformer 48 results not only inan increase in the voltage between the principal electrodes 3 and 4 of.the tube I, but also in a large increase in the light intensity of theoperating lamp 31. As a result, the margin between the illuminationrequired to operate the tube and the illumination at which it does notoperate must be rather large.

The secondlamp 38 and the second photo-cell 32 may be of such structurethat they are more sensitive to variations in the voltage than the firstlamp 31 and the first photo-cell 28. Consequently, an increase in thevoltage supplied to the primary 4| of the transformer 48 causes adecrease in the impedance between the electrodes 2| and 22 of the secondphoto-cell 32 that is relatively larger than the decrease between theelectrodes 2| and 22 of the first photo-cell 28. Hence, the voltagerequired to cause a discharge in the discharge tube I is increased, andthus the fluctuations in the power supply are at least partiallycompensated.

I have found that while, in the earlier trafliccontrol systems, thedecrease in illumination of the operating light 31, necessary to actuatethe system, is 48%, my-improved system operates satisfactorily for adecrease in illumination of only 24%.

In addition to the above discussed advantages, the apparatus shown inFigs. 3 and 4, and, to an even greater degree, the apparatus shown inFig. 6, involve certain features which are of considerable importance.This aspect of the situation may be discussed with reference to themodification shown in Fig. 6.

In the apparatus shown in this view, the anode of the photo-cell 28 isconnected to the junction point of the anode 4 of the discharge device Iand the resistor 30. When the discharge device I is deenergized, thetotal potential of the source 48 is impressed between the cathode 22 ofthe cell 32 and the anode 2| of the cell 28. However, when the dischargedevice I is energized current flows through the resistor 30 and thepotential drop across the photo-cells 28 and 32 is decreased by the dropacross the resistor. The latter potential drop is in general ofconsiderable magnitude and the decrease is therefore comparativelylarge. By reason of the decrease, the photo-cells are protected againstdisruptive discharge and the injuries resulting therefrom at the veryinstant that such protection is necessary, namely, when the dischargedevice I is energized,

It is to be noted that the resistor 30 is an important element inproducing the advantage discussed above. Where the current source is ofthe usual constant-voltage type, the desired result claiming thefeature.

the resistor as current is transmitted through the discharge device I.Hereinafter, I shall refer to a voltage absorbing device" whendiscussing or This expression is used with the understanding that it mayapply to any general element which absorbs voltage. Thus, it may betaken as calling for an element such as the resistor 30 or the load 21.

Although I have shown and described certain specific embodiments of myinvention, I am fully aware that many modifications thereof arepossible. My invention, therefore, is not to be restricted exceptinsofar as is necessitated by the prior art and by the spirit of theappended claims.

I claim as my invention:

1. Translating apparatus comprising an electric discharge device havinga control electrode and a plurality of principal electrodes immersedin agaseous medium, said device having an energized condition and adeenergized condition and being capable only of abrupt transition fromone.

condition to the other, a source of electrical energy for impressingpotentials between the electrodes of said device to maintain said devicein one or the other of said conditions, a photosensitive device coupledbetween the control electrode and a principal electrode of said device,means for energizing said photo-sensitive device to vary the conditionof said electric discharge device, another photo-sensitive devicecoupled between the control electrode and another principal electrode ofsaid electric discharge device and means, to be energized from saidsource, for

energizing said last named photo-sensitive device to suppress variationsin the condition of said electric discharge device that tend to arise byreason of variations in said source.

2. Translating apparatus comprising an electric discharge device havinga control electrode and a plurality of principal electrodes immersed ina gaseous medium, said device having an energized condition and adeenergized condition and being capable only of abrupt transition fromone condition to the other, a source of electrical energy for impressingpotentials between the electrodes of said device to maintain said devicein one or the other of said conditions, a first photosensitive deviceenergized from said source coupled between the control electrode and aprincipal electrode of ,said discharge device, a second photo-sensitivedevice energized from said source coupled between the control electrodeand another principal electrode of said discharge device, saidphoto-sensitive devices having different voltage-sensitivitycharacteristics.

3. Translating apparatus comprising an electric discharge device havinga control electrode and a plurality of principal electrodes immersed ina gaseous medium, said device having an energized condition and adeenergized condition and being capable only of abrupt transition fromone condition to the other, a source of electrical energy for impressingpotentials between the electrodes of said device to maintain said devicein one or the other of said conditions, a first photosensitive deviceenergized from said source coupled between the control electrode and aprincipal electrode of said discharge device, a second photo-sensitivedevice energized from said source coupled between the control electrodeand another principal electrode of said discharge device, saidphoto-sensitive devices having diilerent voltage-sensitivitycharacteristics, whereby the efiects of variations in said voltage onthe electrical condition of said discharge device are neutralized.

4. Translating apparatus comprising an electric-discharge device havinga control electrode and a plurality of principal electrodes immersed ina gaseous medium, said device having an energized condition and adeenergized condition and being capable only of abrupt transition fromone condition to the other, a source of electrical energy for impressingpotentials between the electrodes of said device to maintain said deviceinone or the other of said conditions, a first photosensitive devicecoupled between the control electrode and a principal electrode of saiddischarge device, means energized from said source for subjecting saidfirst photo-sensitive device to radiation, a second photo-sensitivedevice coupled between the control electrode and another principalelectrode of said discharge device and a second means energized fromsaid source and having a difierent radiation characteristic from saidmeans last named for subjecting said second photo-electric device toradiation.

5. An electric discharge device having a control electrode, an anode anda cathode, means for impressing a potential difierence between saidanode and cathode, impedances connected between said control electrodeand each of the other said electrodes and means, responsive to avariation in the terminal potential difierence of the first said meansto decrease the ratio of the impedance connected to the cathode to theimpedance connected to the anode when said potential difierence rises.

6. An electric discharge device having a control electrode and a.plurality of principal electrodes, said principal electrodes beingimmersed in a gaseous medium, means for impressing a potentialdiiierence between said principal electrodes and also between saidcontrol electrode and one of said principal electrodes and lightresponsive means to be energized in response to variations in theterminal potential difference of the first said means to compensate forthe eiiect of said variationsin producing variations in the poten-' tialdifierences impressed between said principal electrodes and in thepotential difierence impressed between said principal electrodes andsaid control electrode.

'1. An electrical circuit comprising a source of electrical energy, atube connected to receive current from said source and equipped with acontrol electrode, an anode and a cathode, and a plurality ofphoto-cells provided each with a cathode and an anode, the cathode ofone of said photocells being connected to the cathode of said tube, theanode of said photo-cell being connected to said control electrode andthe cathode of another of said photo-cells being connected to saidcontrol electrode and the anode of said cell being connected to theanode of said tube, and means to decrease the ratio of the-resistance ofthe firstmentioned photo-cell to that of the last-mentioned photo-cellas the voltage of said source rises.

8. An electrical circuit comprising a source of electrical energy, adevice of the glow discharge type connected to receive current from saidsource and equipped with a control electrode, an anode and a cathode, aplurality of impedances one of which is a photo-cell provided with acathode and an anode, one of said impedances being connected between theanode of said device and said control electrode, and the other saidimpedance being connected between the control electrode and the cathodeof said device, andmeans to cause the ratio of the last-mentionedimpedance to the first-mentioned impedance to decrease when the voltageof said source rises.

9. An electric discharge device having a control electrode, an anode anda cathode, means for impressing a potential difierence between saidanode and cathode, impedances connected between said'control electrodeand each of the other said electrodes and means, responsive to avariation in the terminal potential difference of the first said meansto decrease the ratio of the impedance connected to the cathode to theimpedance connected to the anode when said potential difference rises.

DEWEY D. KNOWLES.

